Speech synthesis by linear interpolation of spectral parameters between dyad boundaries

Recent work of Olive and Spickenagel has shown that pseudo-area parameters used for LPC synthesis can be linearly interpolated between dyad boundaries without producing excessive distortion in synthetic speech. This study investigates whether such interpolation can be done equally successfully on the power spectrum of the speech waveform. The spectrum is of special interest because speech can be synthesized in real time from spectral parameters on readily available programmable digital filters. Our results show that the distortion introduced by dyadic interpolation of spectrum is perceptually significant but it can be reduced considerably by using an additional point within the dyad boundaries for interpolation. The reasons for good quality of speech synthesized from dyadically-interpolated area parameters were also investigated. It was found that formant frequency movements are reproduced fairly accurately after dyadic interpolation. Formant bandwidths however are not reproduced accurately but the bandwidth errors are not as important subjectively.